PHP Review the PHP Tag

CSC 342 - Web Technologies, Spring 2017 PHP Review The PHP Tag PHP source code is typically an HTML document with php tags embedded within it: <? php /* PHP code */ ?> Anything within the opening and closing php tags is assumed to be PHP code and should be executed by the PHP interpreter Basic Syntax Statements must end in a semicolon Variables must start with a $ symbol Line comments are denoted by // Block comments are denoted by /* ... */ keywords, classes, functions and user-defined functions are NOT case sensitive variable names ARE case sensitive Simple Example <!DOCTYPE html> <html > <head > <title>Hello World</title> </head > <body > <? php $message = "Hello world"; echo "$message"; ?> </body > </html > Variable Naming Rules Must start with a dollar sign ($) followed by a letter or the underscore character ( ) Can only contain a-z,A-Z,0-9, and Variable names are case sensitive PHP Types PHP data types: String Number: (Integer and Float) Boolean Array Object NULL PHP is dynamically typed { types of variables do not need to be declared PHP is generally weakly typed { some type conversions are automatic The String Type The string type represents a sequence of characters Categories of string literal: delimited by single quotes ('...') interpolated: delimited by double quotes ("...") The escape character is the backslash (n) The dot (.) operator performs string concatenation Multi-line strings A string can be defined over multiple lines <? php $name = "first_name last name "; ?> Heredoc syntax preserves white space <? php $name = <<<_END first_name last name _END; ?> Heredoc Syntax Rules The <<<TOKEN starts a heredoc The token name is user defined, it typically should be a value not expected to be seen in the string The ending token must be the first thing on the line followed by a semicolon (TOKEN;) There is no need to escape any characters in a heredoc Arithmetic Operators Operator Description Example + Addition $a + 3 - Subtraction $a - 3 * Multiplication $a * 3 / Division $a / 3 % Modulus $a % 3 ++ Increment ++$a -- Decrement --$a Assignment Operators Operator Example Equivalent to = $a = 3 $a = 3 += $a += 3 $a = $a + 3 -= $a -= 3 $a = $a - 3 *= $a *= 3 $a = $a * 3 /= $a /= 3 $a = $a / 3 %= $a %= 3 $a = $a % 3 .= $a .= $b $a = $a . $b PHP Implicit Type Coercion The type of a variable is implicitly converted based on the context in which the variable is used In PHP this is called \Type Juggling" <? php $x = "10"; // string $y = 3.14; // float $z = $x * $y; // float ?> The gettype function returns a string representation of a variable's type Explicit Type Casting (int), (integer) cast to integer (bool), (boolean) cast to boolean (float), (double), (real) cast to float (string) cast to string (array) cast to array (object) cast to object (unset) cast to NULL PHP Constants Constants are similar to variables, but the value cannot be changed once set Syntax <? php define("NAME", "VALUE"); ?> NAME is the name of the constant and is traditionally upper case VALUE is the value assigned to the constant Checking Syntax The syntax of a PHP file can be checked on the command line: php -l FILE.php The -l (lower case L) is short for lint If a syntax error exists, then the error and line number are reported Control Flow The basis of control flow is the boolean type Relational operators return boolean values Types of relational operators Equality Comparison Logical The PHP Boolean Type A boolean expresses a truth value (true or false) The constants TRUE and FALSE are boolean literals FALSE is set to the NULL type Type values that are false when converted to booleans: the boolean FALSE the integer 0 the float 0.0 the empty string "" and the string "0" an array with zero elements the NULL type Equality & Comparison Operators Operator Description Example == equal to $a == 3 === identical to $a === 3 != not equal to $a != 3 !== not identical to $a !== 3 > greater than $a > 3 < less than $a < 3 >= greater than or equal to $a >= 3 <= less than or equal to $a <= 3 Logical Operators Operator Description Example && and $a == 3 && $b == 0 and low-precedence and $a == 3 and $b == 0 || or $a == 3 || $b == 0 or low-precedence or $a == 3 or $b == 0 ! not !($a == $b) xor exclusive or $a xor $b The Equality and Identity Operators The equality operator (==) does implicit type coercion before the comparison The identity operator (===) prevents implicit type coercion, that is, for two operands to be identical, they must have the same type and value Example: <? php $a = "1000" == "+1000"; // TRUE $b = "1000" === "+1000"; // FALSE $a = "1000" != "+1000"; // FALSE $b = "1000" !== "+1000"; // TRUE ?> Selection if, else, and elseif <? php if ($page == "Home") {/* code */} elseif ($page == "About") {/* code */} else {/*code*/} ?> switch <? php switch ($page) { case ("Home"): {/* code */; break;} case ("About"): {/* code */; break;} default: {/* code */; break;} } ?> Iteration while loops do while loops for loops <? php for ($count = 1; $count <= 10; ++$count) { echo "The count is" . $count . "\n"; } ?> PHP Arrays In PHP an array is an ordered map that associates keys with values PHP has two types of arrays Numerically indexed arrays use integers as keys Associative arrays typically use strings as keys Constructing Arrays with Integer Keys push consecutive values to the array <? php $a[] = "one"; $a[] = "two"; $a[] = "three"; ?> using explicit indices <? php $a[0] = "one"; $a[1] = "two"; $a[2] = "three"; ?> Associative Arrays Associative arrays map keys other than integers to values <? php $b['one'] = 1; $b['two'] = 2; $b['three'] = 3; ?> If multiple elements are declared with the same key, then only the value of the last element is used Key Casts A string containing an integer will be cast to an integer A float is cast to an integer A bool is cast to an integer The null value will be cast to an empty string Arrays and objects cannot be used as keys Printing Arrays The print r function prints a human readable representation of an array An element of an array can be used as a variable for string interpolation purposes echo "$a[0]"; If the key is not an integer then the array element must be surrounded by curly braces for string interpolation echo "${b['one']}"; The array keyword Arrays can be assigned with the array keyword <? php $a = array("one", "two", "three"); $b = array('one' => 1, 'two ' => 2, 'three' => 3); ?> The foreach loop The foreach loop can be used to iterate through the values of an array Arrays with integer keys: foreach($a as $element) { echo "$element"; } Associative arrays: foreach($b as $key => $value) { echo "$key: $value"; } Multidimensional Arrays The value of a key can be an array $tic_tac_toe = array( array('X', ' ', 'O'), array('O', 'O', 'X'), array('X', 'O', ' ') ); Some Useful Array Functions is array checks if a variable is an array type count returns the number of elements in an array sort performs an in-place sort of an array explode converts a string into an array Superglobals Superglobals are predefined variables that are provided by the PHP environment $ GET: variables passed to the current script via the HTTP GET method $ POST: variables passed to the current script via the HTTP POST method $ COOKIE: variables passed to the current script via HTTP cookies $ SESSION: session variables available to the current script Defining a PHP Function function function_name([parameter [, ...]]) { // Statements } A definition starts with the word function Next is the name of the function, which must start with a letter or underscore, followed by any number of letters, numbers, or underscores The parentheses are required Zero or more parameters, separated by commas The return keyword The return keyword is used to return a value from a function <? php $x = my_max(10, 5); echo "$x"; function my_max($x, $y) { return ($x > $y) ? $x : $y; } ?> Variable Scope Local variables are accessible in context in which they are defined Global variables are accessible from all parts of the code Static variables are accessible from the context in which they are defined, but retain their values Assigning Variables in Global Scope The value of a global variable can be assigned in a function by using the global statement <? php $a = 10; echo "$a"; f (); echo "$a"; function my_max() { global $a; $a = 5; } ?> Static Variable Example <? php counter (); counter (); function counter() { static $count; echo "$count"; $a = 5; } ?> Including and Requiring Files The include statement includes and evalutes the specified file The include once statement includes and evalutes the specified file only once The require statement is identical to the include statement, but if a failure occurs, the script is halted The require once statement is identical to the include once statement, but if a failure occurs, the script is halted.

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